There may be many reasons for the requirement to tow a submersible and towable body from a vessel, including naval and other military reasons relating to national security and the like; as well as oceanologic and oceanographic testing and exploration. The nature of the towed body, and its size may vary considerably depending on the use to which it is put. In most cases, however, a submersible and towable body is one which is adapted to be flooded with water after it is inserted through the air/water interface from being stowed on board the vessel from which it will be towed; and usually the body is constructed with relatively fragile or frangible areas on it, as compared with the construction of a sea-going vessel. Submersible and towable bodies may, indeed, be substantially acoustically apparent at certain frequencies for sonar or other acoustic exploration and searching operations. The towable body may also carry apparatus for continuously sampling the water which it is being towed. The operational requirements for the submersible and towable body may be such that the apparatus from which the body is launched and recovered, as well as towed, be adapted to operate in very heavy sea states and at very high speeds. Heavy loading on the apparatus due to wave slap, tow-off, and other shock loading, and the requirement to launch and recover a submersible and towable body at high speed, would be expected to result in the production of an apparatus therefore which would be very heavy and massive. Unfortunately, many vessels do not have the deck space or capacity to carry very heavy and bulky equipment.
Certain specific problems relating to the launching and recovery of a submersible and towable body, from a vessel - including such vessels as hydrofoils and ground or surface effect vehicles (air cushioned vehicles) as well as more conventional ocean going trawlers and naval vessels - have required consideration. They include the fact that the submersible and towable body should be launched and recovered from a saddle to which it can be secured with cable tension of the cable from which the body is towed while the body is still beneath the surface of the water and before it is brought through the air/water interface. Further, where the vessel has a high deck, it is desirable to provide launching, towing and recovering apparatus without necessitating extensive modification to the vessel and which can be installed on the vessel in a minimum of time. Means are provided by this invention for tilting the entire deck frame on which the cable winch and the towable body handling apparatus are mounted. A skewable A-frame which includes a transom arm mounted at the aft end of the vessel is therefore contemplated by this invention.
When a body is being towed from a vessel, it is secured at the outer end of the cable which is reeled and unreeled from a winch located on the vessel. At any time while the body is submersed and it is not being securely held into its saddle by the cable which is in tension -- in other words, whenever there is cable unreeled from the winch -- it is necessary to provide cable tension stabilizer means to prevent snap loading of the cable such as when the vessel moves through rough waters. In accordance with the present invention, and considering the usual installation of an apparatus as contemplated by this invention aboard ship, the cable leads forward from the winch over a spooler and cable tension stabilizer assembly which may comprise one or more sheaves, and thence rearwards from the cable spooling assembly to the towing sheave which is situated lengthwise along the cable between the winch and the towed body and which also forms part of the apparatus of the present invention. The cable tension stabilizer may conveniently comprise a shock absorber associated with the cable spooling assembly.
Whenever cable is reeled or unreeled from a winch over a spooling assembly, and the cable does not lead from the reeling point on the winch to the spooling assembly at substantially a right angle to the surface of the drum on which the cable is wound and therefore at a right angle to the axis of rotation of the drum, the angle which results is known as a "fleet angle". Especially when a cable which is being reeled or unreeled from the drum of a winch is in tension, and more especially when the cable is faired, it is desirable to maintain the fleet angle as close to zero as possible. In a preferred embodiment of this invention, as discussed hereafter, the fleet angle is essentially maintained at zero by the use of a multiple sheave assembly which is adapted to move in such a manner as to keep the cable reach from the winch to the cable towing sheave as short as possible; and because of the geometry of the assembly, the fleet angle at the winch is maintained at substantially zero.
It is also desirable to provide a winch construction on which a cable -- especially a faired cable -- may be reeled and unreeled, which is capable of withstanding high side loading but which takes up as little onboard space as possible. Especially in military installations, the requirement for the winch to withstand high athwartships shock is a very real one, and in any event the roll of a ship may cause considerable loading on the winch. A conventional port 1 frame cannot be crossbraced in the usual manner because of the swept area taken up by the drum or drums of the winch, and therefore the vertical supports of such a frame and the athwartship member have to be designed to be very large in order to accommodate the twisting loads which might be encountered. This invention contemplates a winch construction of a "wrap-around" type wherein an enclosure frame substantially encloses the winch drum, with a transverse slot formed in the enclosure and with the winch drum or drums bearingly mounted in the end of the frame. Very substantial athwartships rigidity is thereby achieved in a minimum of athwartships space and with a lower weight. Also, of course, the frame enclosure provides protection of the stowed cable against ice build-up; and because the cable is stowed under tension, considerably less hazard due to cable breakage is afforded for personnel working near the winch.
Where a considerable length of cable is to be stowed by the winch -- for example, in excess of 1,000 feet -- the winch construction may comprise two or more drums which are coaxially mounted. The drums are arranged with a transverse slot in the surface of each drum except the innermost one so that cable may be reeled and unreeled from the multiple drum assembly; with the cable being unreeled serially from the outermost to the inner most drum and reeled serially from the innermost to the outer most drum. However, to maintain alignment of the transverse slots in each of the drums which is outwards of the drum on which cable is being reeled or unreeled, it is necessary to latch those outward drums for nonrotation. Also, because only the innermost drum is driven, it is necessary to latch the innermost drum and any other drums having cable reeled upon them with the drum upon which cable is being reeled at any one time for rotation so as to be driven by the winch drive means. Still further, it is desirable to provide latch means for automatically latching or unlatching adjacent ones of the drum as cable is reeled onto or off those drums without having to stop the outboard or inboard (i.e. unreeling or reeling) movement of the cable relative to the winch. Automatic latching means are therefore provided by this invention which meet the above requirements with respect to non-stop reeling in a multidrum winch.
Because the cable is wound under tension, and because in most circumstances the cable may be faired, it is necessary to provide a multidrum winch assembly wherein the clearance between drums is sufficient to permit stowage of cable on a drum having a transverse slot without interference of the cable on that drum with the cable which is stowed on the drum immediately inwards thereof. Also, it is desirable to reduce the radial loads in the material of the drum to zero load at the edges of the transverse slots. This invention therefore provides a drum construction wherein the lips formed on the transverse edges of each transverse slot are curved inwardly towards the interior of the drum with an apparent radius of curvature being less than the nominal radius of that respective drum. By so doing, a slotted drum construction for a multidrum assembly can be provided having a strength comparable to a conventional, unslotted drum; and therefore the multidrum winch construction is capable of reeling and unreeling and stowing cable which is in tension.
It is desirable when working with a faired cable to provide a slotted drum surface to accommodate that cable. This invention contemplates the provision of a slotted or grooved drum section by the application to the surface of the material from which the drum is formed of an outer layer of relatively flexible material which has a cross-section so as to form the desired grooves at the outer surface of the drum.
This invention also contemplates the provision of a roller box assembly which forms part of the launch and recovery saddle for the submersible and towable body and which can be accommodated to saddles of the non-inverting type. In the usual case, the present invention contemplates an inverting saddle for the most effective and economical structure for launch and recovery of the submersible and towable body at the air/water interface. However, other structures also exist whereby a saddle is rigidly fixed with respect to the horizontal -- at least as defined by the deck of the vessel -- and where the saddle is moved to the air/water interface by means of a pantographic assembly. However, it would be desirable to tow the body from a tow sheave which is intimately associated with the recovery saddle, and also to provide means for maintaining a constant pressure against the nose of a faired cable as it passes from the two sheave to the towed body as it is underwater. This is especially true when the cable is faired so that the body tends to be towed in a position which is very nearly beneath the vessel; and so that the cable pierces the air/water interface (the water surface) in a nearly vertical orientation. Still further, however, is the requirement that a roller box be provided which not only has a nose roller but which has side rollers, one on either side of the cable, and that the roller box be biased so as to maintain a position relative to the cable as it passes through the roller box so that the axes of the side rollers are substantially perpendicular to the axis of the cable. This is especially important when towoff occurs as the vessel turns or rolls, so as to preclude a tendency of the cable to corkscrew. It is also important, during towoff, that the roller box be adapted to absorb sideways loading as the side rollers make contact with the cable.